Four component adhesive blends and composite structures

ABSTRACT

Compositions of matter having properties that make them strong adhesives to various substrates and especially for adhering polypropylene and polyethylene to various polar substrates. These compositions comprise blends of a graft copolymer of a polyethylene backbone grafted with at least one grafting monomer comprising one or more of polymerizable ethylenically unsaturated carboxylic acids of the anhydrides of such acids blended with a blending resin that is a mixture of one or more high density polyethylenes, one or more linear low density polyethylenes and one or more polypropylenes. The disclosure also includes composite structures comprising one or more substrates and a blend of the above as the adhesive in contact with the substrate or substrates and the method of preparing these composite structures. 
     This invention relates to adhesive blends comprising modified polyolefin resins with improved adhesion to substrates and especially polar substrates such as metals, glass, paper, wood and polar polymers such as polyamides, polyureas, polycarbonates, polyurethanes, copolymers of olefins with vinyl esters and with vinyl alcohols, cellulose and its derivatives, etc. These adhesive blend resins can be used in any conventional process for combining dissimilar materials. Examples of these methods are lamination, coextrusion, powder and/or extrusion coating, blow molding, etc., or any combination of these processes. The adhesive blends of this invention also have excellent moisture-barrier properties.

BACKGROUND OF THE INVENTION

It is known that blends of polypropylene (PP) with high densitypolyethylene (HDPE) or low density polyethylene (LDPE) or ethylene vinylacetate copolymers (EVA) and with a high density polyethylene graftedwith suitable unsaturated carboxylic acids or acid derivatives such asanhydrides give adhesion to polyethylene and other olefins as well as topolar polymers and other substrates as listed above. This is disclosedin copending application Ser. No. 178,355 filed Aug. 15, 1980 and Ser.No. 327,278, filed Dec. 4, 1981, both assigned to the same assignee asthe present application.

SUMMARY OF THE INVENTION

The improvements achieved by this invention include the following:excellent bond strength to ethylene-vinyl alcohol copolymer. Theadhesion value is 4-6 lbs/in. compared to less than 2 lbs/in. inconventional blends containing a high content of high densitypolyethylene. The invention results in excellent adhesion to polyolefinssuch as polypropylene and to high and low density polyethylene, superiormoisture barrier properties and excellent adhesion to polyamides andother polar polymers, metals and polar substrates generally.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A blend is made comprising (A) a high density polyethylene resin (HDPE)of density 0.94 to 0.97 g/cc, (B) a polypropylene resin or a copolymercontaining high percentage of propylene units, (C) a low densitypolyethylene resin (LDPE) of density 0.91 to 0.94 g/cc, and (D) apolyethylene grafted with or containing in its main chain unsaturated orsaturated carboxylic acids or acid derivatives such as acid anhydrides,acid chlorides, acid amines, acid imines and the like.

The four component blend gives excellent adhesion to substrates and alsoprovides an excellent moisture barrier. If the application requires evenhigher moisture barrier characteristics, the high density polyethylenecontent in the blend can be increased but lower adhesion to polarsubstrates results. If the application requires superior adhesion topolypropylene, it is advantageous to increase the content ofpolypropylene in the blend. If the object is to obtain even betteradhesion to polar substrates, and moisture barrier properties are nottoo critical, a lower amount of high density polyethylene would beneeded in the blend.

Examples of the methods of using these blends include coextrusion,lamination, coating or a combination of these methods or any othermethod known to those skilled in the art.

The invention also includes composite structures comprising substratesand the adhesive blends of this invention. The composite structure canbe in the form of films, containers, sheets, bottles, tubes, etc.

The term "unsaturated or saturated carboxylic acids or acid derivatives"includes acids, acid salts with metal, acid esters and anhydrides, acidamines, acid chlorides and bromides and any other acid derivatives ofaliphatic, alicyclic, aromatic fused ring, or heterocyclic moieties andcopolymers containing these groups.

The unsaturated carboxylic acids or acid anhydrides used as the graftingmonomers include compounds such as acrylic acid, methacrylic acid,fumaric acid, maleic acid, maleic anhydride, 4-methylcyclohex-4-ene-1,2-dicarboxylic acid anhydride,bicyclo(2.2.2)oct-5-ene-2,3-dicarboxylic acid anhydride,1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid anhydride,2-oxa-1,3-diketospiro(4.4)non-7-ene,bicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride, maleopimaricacid, tetrahydrophthalic anhydride,x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride,x-methylnorborn-5-ene-2,3-dicarboxylic acid anhydride,norborn-5-ene-2,3-dicarboxylic acid anhydride, Nadic anhydride, methylNadic anhydride, Himic anhydride, methyl Himic anhydride and other fusedring monomers described in U.S. Pat. Nos. 3,873,643 and 3,882,194, bothassigned to the assignee hereof.

Cografting monomers as described in U.S. Pat. No. 3,882,194 are alsouseful for preparing the graft copolymers of this invention.

Included among the conjugated unsaturated esters suitable for cograftingare dialkyl maleates, dialkyl fumarates, dialkyl itaconates, dialkylmesaconates, dialkyl citraconates, alkyl acrylates, alkyl crotonates,alkyl tiglates and alkyl methacrylates where alkyl represents aliphatic,aryl-aliphatic and cycloaliphatic groups containing 1-12 carbon atoms.Esters particularly useful in the cografted copolymers of this inventionare dibutyl maleate, diethyl fumarate and dimethyl itaconate. Among theacids and acid anhydrides particularly useful in the cograftedcopolymers of this invention are maleic anhydride, fumaric acid,x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride andbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride.

The term "low density polyethylene" used as blend component (C) includeshigh-pressure low density polyethylene as well as low-pressure linearlow density polyethylene. It is preferable to have a resin density inthe range 0.91 to 0.94 g/cc and a melt index of 0.1 to 50 g/10 min. Themelt indices given here are as determined by ASTM Test Procedure D 1238.Low-pressure linear low density polyethylene is preferred.

Adhesive blends of this invention can be used in composites containingpolar substrates such as nylon, ethylene vinyl alcohol copolymers(EVOH), polyvinyl alcohol (PVA), polyester, polyurethane, metals, etc.These compositions can be just two layers or they can be three or morelayers with materials which adhere to either layer being added to thestructure. For instance, polyolefins like polyethylene (PE), ethylenevinyl acetate copolymers (EVA) or ethylene copolymers with othermonomers, ionomers and polypropylene (PP) can be used in these layers.It is obvious that many combinations can be made by one skilled in theart of using the principles disclosed.

Some examples of these composites are PE/adhesive of thisinvention/nylon, PE/adhesive/ethylene-vinyl alcohol copolymer,PE/adhesive/aluminum, PE/adhesive/steel, PE/adhesive/glass,PE/adhesive/wood, PE/adhesive/leather, PE/adhesive/nylon/adhesive/PE,and PE/adhesive/EVOH/adhesive/PE. Some examples of composites involvingother polyolefins are EVA/adhesive/nylon, ionomer/adhesive/nylon,PP/adhesive/nylon. Obviously, many other combinations of polyolefins andpolar substrates can be prepared by one skilled in the art using theprinciples described above.

Examples of other metal combinations are aluminum/adhesive/aluminum oradhesive/aluminum/adhesive orpolyethylene/adhesive/aluminum/polyethylene. Other metals such ascopper, steel, brass, etc. can also be used. Dissimilar metal examplesare: aluminum/adhesive/copper, aluminum/adhesive/steel,aluminum/adhesive/brass, etc. One could also have combinations in whichone has a metal/adhesive/polar polymer. Examples of these would bealuminum/adhesive/nylon or aluminum/adhesive/EVOH, orsteel/adhesive/nylon/adhesive/steel. Here again, one skilled in the artcan find a number of obvious combinations from the principles describedabove.

These materials can be used to manufacture many different usefularticles. They can be used as packaging film, blow molded bottles,coextruded sheet which can be thermoformed into containers, coatings onglass bottles or wood or metal or even to join two metals, either thesame metal or dissimilar metals, into a lamination.

In preparing the blends in the following examples, any blendingequipment or technique may be used.

All blends preferably contain an antioxidant package.

In most of the specific examples, blends were prepared in anelectrically heated Brabender plasticorder mixer using a scroll typemixer under the following conditions: 400° F., rotor speed of 120 rpm,and total mixing time is 10 minutes.

The resultant blends were then compression molded into filmsapproximately 0.006 inches thick at 350° F. The films were then pressedto the substrate in a Sentinel heat sealer (Model 12 or 12AS) at 40 psipressure. The temperature and time of sealing are varied according tothe conditions desired. The sample is 1 inch in width, the sealing areais 1 square inch. The separation rate is 5 inches per minute. Themaximum peeling load after the initial peak in lbs. per inch of specimenlength is reported. The average of 5 specimens is taken as the T-peelstrength of the adhesive bond. The test angle is 180°.

The procedure herein described is related to ASTM D 1876 (re-appearance1978) with the following differences:

1. The test panel in ASTM D 1876-72--12 inches long by 6 inches wide.The first 3 inches of length are bent back to form a 90° bend.

2. The peel strength is determined from the autographic curve for thefirst 5 inches of peeling after the initial peak.

3. The average peeling load in lbs/in of the specimen width required toseparate the adherent is reported.

EXAMPLES EXAMPLES 1-6

An electrically heated Brabender mixing unit was used for blendingvarious weight ratios of a high density polyethylene (HDPE) of a meltindex 0.1 g/10 min. and a density of 0.944 g/cc, a polypropylene (PP) ofmelt index 0.54 g/10 min. and a density of 0.9 g/cc, a linear lowdensity polyethylene (LLDPE) of a melt index of 2.5 g/10 min. and adensity of 0.918 g/cc and a high density polyethylene (HDPEg) graftedwith x-methyl bicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride,such that the grafted high density polyethylene has a melt index of 1.5g/10 min. and a graft level of 1.5 wt.%. The blends were tested foradhesion to films of ethylene-vinyl alcohol copolymer (EVOH) andaluminum (Al) with a heat sealer set at 430° F. for 1 sec. and topropylene (PP) film at 500° F., 5 sec. The results obtained for each ofthe various compositions are listed below:

    __________________________________________________________________________                                   Adhesion                                                                            Adhesion                                        Percentage of Blend                                                                           Adhesion to                                                                           to    to                                       Example No.                                                                          HDPE                                                                              LLDPE                                                                              PP                                                                              HDPEg                                                                              EVOH (lbs/in)                                                                         Al (lbs/in)                                                                         PP (lbs/in)                              __________________________________________________________________________    1      40  10   30                                                                              20   1.6     --    --                                       2      40  30   10                                                                              20   1.5     --    --                                       3      45  15   30                                                                              10   1.6     --    --                                       4      45  30   10                                                                              15   1.8     --    --                                       5      40  20   20                                                                              20   5.9     6.1   0.9                                      6      10  35   35                                                                              20   >7.0.sup.FT                                                                           4.7   1.4                                      __________________________________________________________________________     .sup.FT film tear                                                        

EXAMPLE 7

In addition to the grafted high density polyethylene in the examplesabove, a linear low density polyethylene grafted with x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride (LLDPEg) wasused. All the other components used for this example are the same asthose used for Example 5. The heat sealing to ethylene vinyl alcohol(EVOH) copolymer films was carried out with the sealer set at 430° F.and 1 sec. and the adhesion levels obtained are given below:

    ______________________________________                                        Exam-                              Adhesion                                   ple   Percentage in Blend          to EVOH                                    No.   HDPE    LLDPE    PP  HDPEg  LLDPEg (lbs/in)                             ______________________________________                                        7     40      20       20  10     10     5.9                                  ______________________________________                                    

EXAMPLES 8-10

The high density polyethylene used in Examples 1-6 was replaced byanother high density polyethylene which had a melt index of 2.7 g/10min. and a density of 0.958 g/cc. The blends were prepared as in Example1 and heat sealed to ethylene-vinyl alcohol copolymer (EVOH) and HDPEfilms with the sealer set at 430° F. and 1 sec. The adhesion data inlbs/in. is given below for each of the blends:

    ______________________________________                                        Example                                                                              Percentage in Blend Adhesion to                                        No.    HDPE    LLDPE    PP  HDPEg  EVOH  HDPE                                 ______________________________________                                        8      40      30       10  20     2.4   >10.0.sup.CNS                        9      40      10       30  20     >3.1.sup.FT                                                                         >8.0.sup.CNS                         10     40      20       20  20     >4.0.sup.FT                                                                         >7.6.sup.CNS                         ______________________________________                                         .sup.FT film tear                                                             .sup.CNS Could Not Separate                                              

EXAMPLE 11

The linear low density polyethylene component was changed to one thathad a melt index of 1 g/10 min. and a density of 0.924 g/cc. The ratiosand the other components used were the same as in Example 5. Theadhesion to EVOH film when heat sealed at 430° F. and 1 sec. was 1.5lbs/in. and was 2.3 lbs/in. when heat sealed to a nylon 6 film under thesame sealer setting conditions.

EXAMPLE 12

When the high density polyethylene in Example 10 was replaced by anotherwith a density of 0.960 g/cc and a melt index of 1.0 g/10 min. Theadhesions to EVOH film and nylon 6 film were 3.7 and 2.9 lbs/in.respectively when the heat sealer was set at 430° F. and 1 sec.

EXAMPLES 13-16

An electrically heated Brabender mixing unit was used for blendingvarious weight ratios of a high density polyethylene (HDPE) of meltindex 1.0 g/10 min. and of density 0.960 g/cc, a polypropylene (PP) ofmelt index 0.54 g/10 min. and a density of 0.9 g/cc, a linear lowdensity polyethylene (LLDPE) of density 0.919 g/cc and melt index 1.9g/10 min. and a high density polyethylene (HDPEg) grafted with x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic anhydride such that thegrafted HDPE had a melt index of 1.5 g/10 min. and a graft level of 1.5wt.%. The blends were tested for adhesion after heat-sealing to films ofnylon 6 and ethylene-vinyl alcohol (EVOH) copolymers at 430° F. and 1sec. and to a film of polypropylene at 500° F. for 5 sec. The results inlbs/in. are given below for the various blends prepared.

    ______________________________________                                        Example                    Adhesion to                                        No.    HDPE    LLDPE    PP  HDPEg  EVOH  Nylon PP                             ______________________________________                                        13     10      40       40  10     2.9   3.9   2.9                            14     10      40       30  20     2.4   >4.3.sup.FT                                                                         0.7                            15     10      30       40  20     0.9   3.1   2.5                            16     40      20       20  20     0.6   3.3   1.0                            ______________________________________                                         .sup.FT film tear                                                        

EXAMPLE 17

A blend, similar to that in Example 11 except prepared on a largeBanbury mixing unit, was coextruded separately with polypropylene blockcopolymer resin and with ethylene-vinyl alcohol copolymer. With thepolypropylene block copolymer, the adhesion obtained was 2.2 lbs/in withan elongation, while with ethylene-vinyl alcohol copolymer, the blendgave an adhesion value of 2.6 lbs/in.

EXAMPLE 18

A blend, similar to that in Example 11 except that the linear lowdensity polyethylene was substituted by branched low densitypolyethylene of density 0.922 g/cc and of melt index 2.0 g/10 min. Theadhesion obtained when heat-sealed to an ethylene-vinyl alcoholcopolymer film with the heat sealer set at 430° F. and 1 sec. was 3.3lbs/in. The same blend gave 6.0 lbs/in with film tear when tested to anethylene-vinyl alcohol copolymer film with the heat-sealer set at 500°F. and 1 sec.

Glossary of Terms

EVOH--ethylene-vinyl alcohol copolymer

HDPE--high density polyethylene

LDPE--low density polyethylene

LLDPE--linear low density polyethylene

HDPEg--HDPE graft copolymer

LLDPEg--LLDPE graft copolymer

PP--polypropylene

I claim:
 1. A modified polyolefin blend consisting essentially of:(A)HDPE having a density of about 0.94-0.97 g/cc; (B) at least onepolypropylene polymer or copolymer; (C) LDPE having a density of about0.91-0.94 g/cc; and (D) a polyethylene polymer grafted with at least onegrafting monomer polymerizable ethylenically unsaturated carboxylic acidor acid derivative.
 2. The blend of claim 1 wherein said propylenepolymer or copolymer comprises propylene homopolymers and copolymers ofpropylene and one or more unsaturated aliphatic hydrocarbons.
 3. Theblend of claim 1 wherein said polypropylene polymer comprises acopolymer of propylene and ethylene.
 4. The blend of claim 1 whereinsaid grafting monomer comprises at least one of acrylic acid,methacrylic acid, fumaric acid, maleic acid, itaconic acid, citraconicacid, mesaconic acid, maleic anhydride, 4-methylcyclohex-4-ene-1,2-dicarboxylic acid anhydride,bicyclo(2.2.2)oct-5-ene-2,3-dicarboxylic acid anhydride,1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid anhydride,2-oxa-1,3-diketospiro(4.4)non-7-ene,bicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride, maleopimaricacid, tetrahydrophthalic anhydride, norborn-5-ene-2,3-dicarboxylic acidanhydride, Nadic anhydride, methyl Nadic anhydride, Himic anhydride,methyl Himic anhydride, and x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride.
 5. The blendof claim 1 wherein said unsaturated or saturated carboxylic acids oracid derivatives of (D) comprise the acids, metal salts of said acids,acid esters, acid anhydrides, acid amines, acid halides and acidderivatives of aliphatic, alicyclic, aromatic fused ring, heterocyclicmoieties and copolymers containing one or more of these groups.
 6. Theblend of claim 1 wherein the polyethylene of (D) comprises ethylenehomopolymers and copolymers of ethylene with one or more of butene,hexene, octene, 4-methyl pentene-1 or other unsaturated aliphatic oraromatic hydrocarbons in the density range 0.91 to 0.97 g/cc.
 7. Theblend of claim 6 wherein the polyolefin of (D) comprises linearpolyethylenes.
 8. The blend of claim 1 wherein said HDPE of (A)comprises an ethylene homopolymer and copolymers of ethylene with olefinmonomers containing 3-15 carbon atoms.
 9. The blend of claim 8 whereinsaid HDPE has a density of about 0.94-0.97 g/cc and a melt index ofabout 0.01-50 g/10 min.
 10. The blend of claim 1 wherein the propylenepolymer of (B) comprises propylene homopolymers, copolymers orterpolymers containing less than 40% of a polymerizable comonomer. 11.The blend of claim 1 wherein said LDPE of (C) comprises high pressurelow density polyethylene or low pressure linear low densitypolyethylene, each having a density of about 0.91-0.94 g/cc and a meltindex of 1.0-50 g/10 min.